Vacuum-tube oscillator



Aug. 23, 1 27. 1,639,671

w. SCHAFFER VACUUM TUBE OSCILLATOR Fi led Nov 16, 1922 I 5 wventozWALTER SCHAFFER abtommgv 2 7 1 1M Patented Aug. 23, 1927.

UNITED STATES PATENT OFFICE.

WALTER SGHAFFER, F BERLIN, W. 11, GERMANY, A SSIGN OR '10 GESELLSCHAFTFIIR DRAHTLOSE TELEGRAPHIE M. H. HALLESGHES, OF BERLIN, GERMANY, A

' CORPORATIOI\T OF GERMANY.

VACUUM-TUBE OSCILLATOR.

Application filed November 16, 1922, Serial No. 801,281, and in GermanyNovember 21, 1921.

As is well known, the best operating conditions in the use of tubesenders are attained when both the anode coupling circuitand the gridcoupling circuit have/definite values suitable for the circumstancesunder which the sending is effected, The type of as the grid couplingsare concerned, the ar-' rangements heretofore provided. are verysensitive. For this reason it is usually sufficient if, in operating asender provided for a wide range of wave lengths, the anode cou pling isvaried step by step, so that a single adjustment of the anode couplingis made for a number of wave lengths. On the contrary, usually acontinuous changing of the grid coupling is necessary, that 1s, the gridcoupling must be changed whenever the wave length is changed. If thegrid coupling becomes too loose, then the output of the tube drops to aconsiderable extent; if it is too tight, then the internal tube lossesincrease and the tubes are thereby endan-, 'gered. Arrangements for thecontinuous varying of the grid coupling are rather expensive.

If so-called intermediate circuit senders are used in which theintermediate circuit is arranged as a well known three-point circuit,then the tube coupling may be left mechanically unchanged in a senderthat is suitable e. g. for four wave lengths i'. c.5100 to 2000 meters.However, in this case the coupling conditionsof the tubes are not t ebest for all the wave lengths. They w 11 vary more or less. Thisvariation is the greater, the greater the high frequency resistance ofthe intermediate circuit. The adjustment is eflecte'd in such a mannerthat the best couplings are-tuned for the lon est wave. When shorterWaves are used t en the anode coupling increases. This in itself is onlyslightly harmful, if at all, but at the It is further known that theanode 1 same time the grid coupling increases with serious lossofefficiency of the sender tube.

It is desirable to provide means in send ers having variable gridcoupling for changing the grid couplings without harmful efthis that acondenser is connected in the I grid circuit, in an itself well knownmannei', and a resistance is connected in parallel with the condenser.In accordance with the present 1nvent1on,. this resistance is madevariable whereby the harmful effect of too drawing, the grid circuitincludes a condenser 1 with which a variable resistance 2 is connectedin parallel. This resistance operates in the following manner:

The grid of the oscillating tube is as is well known, charged, and thischarge must flow oif through the resistance 2. Due to this a potentialwill arise at the terminals of the resistance which affects the gridnegatively. In Fig. 2, time is represented on the abscissa. The usefulvalues of the grid potential, the anode current and the anode potentialare indicated on the ordinate. The curve Vg denotes the grid potential.The curve to represents the anode current and the curve Va theanodepotential. V9 is the value of the grid voltage corresponding to currentvalue w atwhich the current to reaches'the saturation point. If theampliis produced by Which the zero line of V9 is pushed downwards, andthe alternating curve Vg. will be' obtained which again reaches only tothe potential Vg for which the saturation point of do is attained. B'y

assuming a correct anode coupling we will now have a certain griddischarge direct current. This-may be easily measured by means of aDeprez instrument which'should be connected in the branch containing theresistance-2. vIf the grid potential Vg be.- comes too large then thisgrid direct current will also increase; Ifthe grid potential isregulated until it reaches its initial value by increasing theresistance 2,,then the original favorable conditions will be obtained.

The above described arrangement for baluncingthe grid potential thatinfluences the tubes may, for example, be used in the well knowntelephone circuit arrangement, shown in Fig. 3, 1n which the speechpotential is impressed on the grid of the generator tube.

In parallel with the condenser l, I provide in series a variableresistance 2, a speech transformer 5 and two air core choke coils 3 and4.- The primary winding of the transformer is provided in a circuitcomprising the telephone transmitter '6 and the battery 7 therefor. Asis well known, this circuit arrangement will operateproperly if in itsnormal condition the saturation value of thegrid potential is notreached, this occurring only when additional positive speech potentialis impressed on the grid. When negative speech potential. is impressedon thegrid, the antennae current will decrease; The

' grid coupling must therefore be more loosely adjusted in the case oftelephony than in telegra hy'. Relatively slight variations must be eected, and it would be too complicated if it were desired to make thegrid potential variable by varying the coupling of the grid to theoscillating-circuit or the like.

7 It is much simpler to vary the effect of the tube arranged to produceoscillations, a grid condenser in the grid circuit of said tube, acircuit consisting of a high frequency choke coil, a grid leak,a sourceof modulating potential, all in series, across said condenser.

3. In a circuit arrangement, a thermionic tube arranged to produceoscillations, a grid condenser in the grid circuit of said tube, meansfor applying modulatingpotential' to said condenser, and meansforpreventing the inflow of carrier current into said first means: I r

I 4:. In a circuit'arrangement, a thermionic tube arrangedto'produce'oscillations, a grid condenser in.the grid circuit of'said'tube, a

coil, and a source of modulating potential in series across saidcondenser.

5.'In a circuit arrangement, a thermionic tube havingits input andoutput circuits eoupled'to produce oscillations by an inductance coilforming althree point coupling, a grid condenser. shanted by a variablegrid condenser, means for applying modulating potential to saidcondenser, and means for preventing the inflow of carrier current intosaid first means.

-' WALTER SOHAFEER' circuit including a high frequency choke I

